Can't access refs on ComponentDidMount

Question

I am trying to select all the text in a textarea when a component loads using React v16.3.1

Following the Refs docs I have a basic sample but this.textarea is always undefined, if I change this sample to execute the same code on a button click it works fine.

So whats going on? I had expected that after mounting the component should be available?

Sample code:

import React from "react";

class Hello extends React.Component {
  constructor(props) {
    super(props);
    this.textarea = React.createRef();
  }

  componentDidMount = () => {
    this.textarea.current.select();
  };

  render() {
    return (
      <div>
        <textarea
          className="form-control"
          defaultValue="the quick brown fox."
          ref={this.textarea}
        />
      </div>
    );
  }
}

From package.json:

"react": "^16.3.1",
"react-dom": "^16.3.1",

Thanks

Answer 1

The documentation says:

Note

The examples below have been updated to use the React.createRef() API introduced in React 16.3. If you are using an earlier release of React, we recommend using callback refs instead.

If you are using an earlier release of React, u need use callback refs

class App extends React.Component {
  constructor(props) {
    super(props);
    this.textarea = null;

    this.setTextareaRef = element => {
      this.textarea = element;
    };
  }

  componentDidMount = () => {
    if (this.textarea) this.textarea.select();
  };

  render() {
    return (
      <div>
        <textarea
          className="form-control"
          defaultValue="the quick brown fox."
          ref={this.setTextareaRef}
        />
      </div>
    );
  }
}

ReactDOM.render(<App />, document.getElementById('root'));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="root"></div>

Using React 16.3

class App extends React.Component {
  constructor(props) {
    super(props);
    this.textarea = React.createRef();
  }

  componentDidMount = () => {
    this.textarea.current.select();
  };

  render() {
    return (
      <div>
        <textarea
          className="form-control"
          defaultValue="the quick brown fox."
          ref={this.textarea}
        />
      </div>
    );
  }
}
ReactDOM.render(<App />, document.getElementById('root'));

<script src="https://unpkg.com/[email protected]/umd/react.production.min.js"></script>
<script src="https://unpkg.com/[email protected]/umd/react-dom.production.min.js"></script>
<div id="root"></div>